Tides and Our Moon’s Origin

Scientists have been wondering how our moon formed, and why its orbit isn’t over Earth’s equator.

It looks like our moon formed after something about the size of Mars hit Earth, roughly 4,500,000,000 years back.

But the giant-impact hypothesis didn’t explain why our moon orbits Earth only five degrees away from Earth’s orbital plane. The math had said that our moon would be orbiting pretty much over Earth’s equator.

God is Large and In Charge

Then I see something like that billboard. The photo, from a Reddit post, was taken on I-75 in Florida back in 2014.

Someone had pretty much the same display on I-94 near my town earlier this year. That billboard advertised ‘Heaven or Hell’ the last time I drove by, probably for the same group.

I appreciate their concern for the souls of travelers, but not their apparent insistence that salvation depends on rejecting what we’re learning about God’s creation.

I think that God is large and in charge, and creating a universe which follows knowable physical laws. This universe is changing: in a “state of journeying” toward perfection. (Catechism of the Catholic Church, 268, 279, 299, 301–308)

Wondering where we came from and where we’re going isn’t idle curiosity. We’re “called to a personal relationship with God,” and can learn something of God by studying God’s creation. (Catechism, 32, 282–289, 299, 301)

This isn’t a new idea:

“Question the beauty of the earth, question the beauty of the sea, question the beauty of the air…. They all answer you, ‘Here we are, look; we’re beautiful.’…
“…So in this way they arrived at a knowledge of the god who made things, through the things which he made.”
(Sermon 241, St. Augustine of Hippo (ca. 411) (from www.vatican.va/spirit/documents/spirit_20000721_agostino_en.html (December 6, 2016))

We’ve been finding answers to some questions about this world — uncovering quite a few new questions in the process. I think accepting our increasing knowledge as opportunities for admiration of God’s work makes sense. (Catechism, 283, 341)

I think shouting for joy makes sense, too.

“The heavens declare the glory of God; the sky proclaims its builder’s craft.
“One day to the next conveys that message; one night to the next imparts that knowledge.”
(Psalms 19:2–3)

“Shout with joy to the LORD, all the earth; break into song; sing praise.”
(Psalms 98:4)

Understanding and Stewardship

We can’t fully understand God.

The Creator is “…incomprehensible, almighty and ineffable … a mystery beyond words.” It’s like St. Augustine of Hippo said:1 “If you understood him, it would not be God.” (Catechism, 202, 230)

This universe may be another matter. Part of our job is taking care of this world. Learning about the universe, and applying that knowledge, is part of our job. (Genesis 1:28; Catechism, 339, 952, 2292–2295, 2402–2405, 2415–2418, 2456)

Living With Reality, and Loving It

We’ve known that the universe is big, old, and changeable, for millennia:

“Of old you laid the earth’s foundations; the heavens are the work of your hands.
“They perish, but you remain; they all wear out like a garment; Like clothing you change them and they are changed,
“but you are the same, your years have no end.”
(Psalms 102:26–28)

“4 Indeed, before you the whole universe is as a grain from a balance, or a drop of morning dew come down upon the earth.
“But you have mercy on all, because you can do all things; and you overlook the sins of men that they may repent.”
(Wisdom 11:22–23)

Immanuel Kant published a more detailed speculation in 1755, and so did Pierre-Simon Laplace a few decades later. We don’t know exactly how the process works. But the nebular hypotheses is still the model that fits what we’ve been observing.

1. When Planets Go Splat!

(From Robin Canup, SwRI; via Astronomy Now, used w/o permission.)
(“The giant-impact theory suggests that the Moon formed out of the debris left over from a collision between Earth and an astronomical body the size of Mars….”
(Astronomy Now))

“New theoretical modelling of the ancient history of the Earth and the Moon suggests that the giant collision that spawned our natural satellite may have left Earth spinning very fast, and with its spin axis highly tilted.

“Computer simulations of what followed the collision, sometimes referred to as the ‘big whack,’ show that following this event, and as the young Moon’s orbit was getting bigger, the Earth lost much of its spin as well gained a nearly upright orientation with respect to the ecliptic. The simulations give new insight into the question of whether planets with big moons are more likely to have moderate climates and life.

” ‘Despite smart people working on this problem for fifty years, we’re still discovering surprisingly basic things about the earliest history of our world,’ says Matija Cuk a scientist at the SETI Institute and lead researcher for the simulations. ‘It’s quite humbling.’…”

Researching this post, I learned that some folks don’t like what’s happening to Earth’s moon. Apparently they say it can’t be doing what it’s doing, because the Bible doesn’t say so. I’m sure they’re sincere. I’m also quite sure that they’re wrong.

Like I keep saying, I’m a Christian and a Catholic. I take the Bible, Sacred Scripture, very seriously. But I don’t assume that the Bible is a science textbook, and I do prefer taking reality ‘as is.’5

Tidal Acceleration and the Leap Second

It wasn’t until the mid-19th century that astronomers decided that their observations and math were right.

Earth’s days were getting slightly longer, our moon’s orbit was getting slightly larger, and the process had been going on for a very long time.

The gist of it is that Earth’s rotation puts the ocean’s tidal bulge slightly ahead of the Earth-moon line. This transfers angular momentum — pulls on the moon — slowing Earth’s daily spin, and boosting the moon into a higher orbit.

The effects are negligible over a human lifetime, unless you’re one of the folks who maintain the UTC — there’s a story6 behind that acronym — clocks. Earth’s drift away from International Atomic Time is why they added the leap second in 1972.

Earth’s day and our moon’s orbital period would eventually be the same, with one side of Earth always facing the moon. If, that is, our sun wasn’t slowly getting warmer. And that’s yet again another topic.7

2. (Almost) “Tying Up All the Loose Ends”

(From Douglas Hamilton, via ScienceDaily, used w/o permission.)
(“In the ‘giant impact’ model of the moon’s formation, the young moon began its orbit within Earth’s equatorial plane. In the standard variant of this model (top panel), Earth’s tilt began near today’s value of 23.5 degrees. The moon would have moved outward smoothly along a path that slowly changed from the equatorial plane to the ‘ecliptic’ plane, defined by Earth’s orbit around the sun. If, however, Earth had a much larger tilt after the impact (~75 degrees, lower panel) then the transition between the equatorial and ecliptic planes would have been abrupt, resulting in large oscillations about the ecliptic. The second picture is consistent with the moon’s current 5-degree orbital tilt away from the ecliptic.”
(ScienceDaily)

“The moon, Earth’s closest neighbor, is among the strangest planetary bodies in the solar system. Its orbit lies unusually far away from Earth, with a surprisingly large orbital tilt. Planetary scientists have struggled to piece together a scenario that accounts for these and other related characteristics of the Earth-moon system.

“A new research paper, based on numerical models of the moon’s explosive formation and the evolution of the Earth-moon system, comes closer to tying up all the loose ends than any other previous explanation. The work, published in the October 31, 2016 Advance Online edition of the journal Nature, suggests that the impact that formed the moon also caused calamitous changes to Earth’s rotation and the tilt of its spin axis….

The U. of Maryland piece ends with Douglas Hamilton’s sensibly-cautious view of what the team accomplished:

“…’There are many potential paths from the moon’s formation to the Earth-moon system we see today. We’ve identified a few of them, but there are sure to be other possibilities,’ [University of Maryland’s Douglas] Hamilton said. ‘What we have now is a model that is more probable and works more cleanly than previous attempts. We think this is a significant improvement that gets us closer to what actually happened.’ ”
(University of Maryland, Science Daily)

We’ve come a long way since 1898, when George Darwin8 said that Earth and Earth’s moon might have started as a single rapidly-spinning body. Centrifugal force could have caused the Earth/Moon to split.

The idea made sense, and fit what scientists were learning about changes in our moon’s orbit. One of my high school textbooks included the ‘fission’ explanation for the moon’s formation, among others. It said the Pacific Ocean could be a scar left by the event.

George Darwin couldn’t get his math to bring the early moon back to Earth’s surface. But the fission idea, and suggestions that Earth captured the moon, looked better than many others until 1946.

That’s when Harvard’s Reginald Aldworth Daly produced math that said a whacking great impact could have resulted in today’s Earth and moon.

The Plot Thickens

The story gets a bit complicated at that point, partly because scientists have been on a steep learning curve over the last few decades.

Today’s models for planetary formation, based on what we’ve been observing, say that collisions of planet-size bodies were very likely in the early Solar System.9

I don’t know if I like, or dislike, the idea of the early Solar System playing bumper cars with planets. But what I think doesn’t matter.

3. Looking Beyond Earth’s Moon

(From NASA, via UC Davis, used w/o permission.)
(“Earth and Moon formed following a massive collision billions of years ago. A new theory answers questions about their composition and the Moon’s orbit.”
(UC Davis))

“Earth’s moon is an unusual object in our solar system, and now there’s a new theory to explain how it got where it is, which puts some twists on the current ‘giant impact’ theory. The work is published Oct. 31 in the journal Nature

“The moon is relatively big compared to the planet it orbits, and it’s made of almost the same stuff, minus some more volatile compounds that evaporated long ago. That makes it distinct from every other major object in the solar system, said Sarah Stewart, professor of earth and planetary sciences at the University of California, Davis, and senior author on the paper….”

Back then, folks who ‘believed in’ flying saucers were making it hard for scientists to discuss what we call exobiology and astrobiology without getting labeled as crackpots.10

That was then, this is now, and the UC Davis piece says that Stewart’s former postdoctoral fellow, Matija Ćuk, is “now a scientist at the SETI Institute in Mountain View, California.”

About SETI, the search for extraterrestrial intelligence, I don’t ‘believe in’ extraterrestrial life, or extraterrestrial intelligence. As of this week, I don’t know whether or not we have neighbors. (September 16, 2016)

Many discussions of SETI assume that everybody uses radio for long-distance communication, and is as chatty as we are, and that’s still another topic. (September 18, 2016; September 16, 2016)

Getting back to Earth’s moon and oddness, our own planet is more than a little unusual. Earth is the densest planet in the Solar System, the only one with readily-observable liquid water on the surface, and still the only planet known to support life.11

Finding “Wonderful Things”

Some protoplanetary disks, like HL Tauri’s, are close enough for astronomers to observe. HL Tauri’s disk is big, almost three times as large as Neptune’s orbit.

Scientists weren’t expecting to see evidence of planets forming in such a young star’s disk, so there’s more to learn: much more. (“eso1436,” ESO (November 6, 2014))

That’s fine by me. I’d be disappointed if it seemed that we finally had all the answers about this universe.

As it is, I think we’re in the process of learning what some of the questions are. We live in a universe filled with wonders, a cosmic puzzle collection that we’ve barely started solving.

What we learn over the next decade, century, millennium, and beyond, will almost certainly upset some folks. People are like that, but not all people. I’m pretty sure that those of us who want to know what’s over the horizon will keep looking: and finding “wonderful things:”

1That’s not exactly what St. Augustine said, of course. Augustine of Hippo lived about 16 centuries back, long before my language existed. Here’s what he said, in Latin, in ‘sermon 52,’ with what I think is a good-enough translation:

“What shall I say, brothers and sisters, of God? For if that which you want to say, if you understood him, it is not God….”
(St. Augustine of Hippo, via Si comprehendis non est Deus, Wikipedia (Italian))

6 “UTC” stands for Coordinated Universal Time, temps universel coordonné in French. A person might think that we’d call it CUT, or TUC. But some folks who set it up spoke French, others spoke English, and there’s a history going back at least to the and Norman Conquest, and that’s — another topic.

Anyway, it’s abbreviated as UTC, instead of TUC or CUT, because English speakers originally proposed CUT, while French speakers said it should be TUC. Folks finally settled on UTC, an acronym which would be equally acceptable — or disliked — by both parties.

My opinion is that we should call it “ET,” for Earth Time, but it’s probably too early for that. Besides, quite a few folks probably still remember that movie and there’s that long-running television show.

Astronomers use Terrestrial Time, which I think is a step in the right direction.

We’re still using leap seconds to keep UT1, the most commonly-used version of UTC, within 0.9 seconds of Solar time at a virtual point on Earth’s surface.

Eventually, Earth Time may be defined as something other than where the sun is, relative to a spot on an island off the European coast — or maybe not. Our current setup puts the International Date Line near the middle of this planet’s largest body of water: which is convenient.

7If our current educated guesses are spot-on accurate, Earth’s oceans will start evaporating about 1,000,000,000 years from now. By then, we’ll have found out whether WR 104 is aimed at us, and probably will have deflected several ‘extinction event’ asteroids. I suspect there’ll be a lively debate about whether to move Earth, adjust our sun, or evacuate this planet. That’s assuming we’re still interested in such things. A billion years is a long time:

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About Brian H. Gill

I'm a sixty-something married guy with six kids, four surviving, in a small central Minnesota town. I mostly write and make digital art. I'm only interested in three things: that which exists within the universe; that which exists beyond; and that which might exist.

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